1. Technical Field
The present invention relates to a wooden member joint structure for use in joining a wooden column to a mating member, such as a wooden beam or foundation, in a wooden building, and, more particularly, to a structure in which a screw member threaded into a wooden member is joined to a mating member via a joint device.
2. Related Art
It is proposed to join a wooden column to a wooden beam, foundation or the like by a so-called rigid joint that allows a bending moment to be transferred therebetween to form a skeleton having a rigid-frame structure in a wooden building. When a horizontal force is repeatedly applied to such a structure alternately in opposite directions during an earthquake, for example, a bending moment acts on the joint between the column and the beam or foundation. The joint needs to maintain sufficient strength against such a bending moment.
A joint structure for a rigid-frame structure using a wooden column is disclosed in Patent Literature 1, for example.
In this joint structure, the column is joined to the foundation via joint devices at two locations at the lower end of the wooden column. The joint structure has the following configuration.
Two screw members having a hollow hole axially extending from one end face thereof are axially threaded into a lower end of the column. A long bolt is inserted into the hollow hole of each screw member, and the upper end of the long bolt is threadedly engaged with the bottom of the hollow hole. In this way, the upper end of the long bolt is connected to the corresponding screw member, and the lower end of the long bolt is connected to a joint device coupled to the foundation. Specifically, an intermediate nut and a fastening nut are threadedly engaged with a male thread formed at the lower end of the long bolt, and the joint device is coupled to the screw member by clamping the joint device sandwiched between the intermediate nut fastened until it firmly abuts against the end face of the screw member and the fastening nut.
In the above joint structure, when a large bending moment is applied to the lower end of the column, an upward pulling force is applied to the location where one of the screw members is threaded into the wooden column and a tensile force is applied to the long bolt threadedly inserted into the hollow hole of the screw member. In addition, a compressive force is applied between the other screw member and the joint device via the intermediate nut. The long bolt to which the tensile force is applied undergoes elongation in such a manner that it is pulled out of the hollow hole of the screw member, and tensile stress causes plastic deformation of the long bolt when the elongation exceeds the elastic region. After that, when a bending moment in the opposite direction is generated, deformation occurs in such a direction that the lower end of the column is pressed against the joint device and a compressive force is applied to the long bolt, which has undergone plastic deformation caused by the tensile stress. In other words, the upper surface of the joint device is pressed against the intermediate nut and a compressive force acts to press the long bolt into the hollow hole of the screw member, and the intermediate nut is therefore returned to the original position where it abuts against the screw member.
In this way, the column is held joined to the foundation via the joint device in the joint structure even when a bending moment is repeatedly applied to the joint alternately in opposite directions.
[Patent Literature 1] JPA-Publication No. 2007-077611
In the joint structure disclosed in Patent Literature 1, even when a bending moment is repeatedly applied to the joint alternately in opposite directions as described above, the joint between the column and the foundation can be maintained and the energy of earthquake motion can be absorbed by plastic deformation of the long bolt.
However, there is the following problem desired to be solved about threading the screw member axially into the column in the above joint structure.
It is desired that the long bolt is previously inserted into the hollow hole of the screw member with its proximal end being threadedly engaged with the bottom of the hollow hole and the intermediate nut is also previously threadedly mounted on the distal end of the long bolt and fastened until it firmly abuts against the lower end face of the screw member when the screw member is threaded into the wooden column. When the long bolt is threadedly engaged with the bottom of the hollow hole and the intermediate nut is fastened after only the screw member is threaded into the wooden column, it is difficult to fasten the intermediate nut until it firmly abuts against the screw member because the rotation of the screw member cannot be constrained. Thus, the screw member needs to be threaded into the column after the long bolt has been threadedly engaged with the bottom of the hollow hole and the intermediate nut has been fastened. In this case, however, it is difficult to thread the screw member into the column such that the lower surface of the intermediate nut is generally flush with the mating surface of the column with the joint device. In other words, the torque applied to thread the screw member into the column cannot be applied to the intermediate nut or directly to the screw member.
In addition, partly because the intermediate nut has to be threadably mounted on the long bolt after the long bolt is threadedly inserted into the hollow hole of the screw member and partly because the joint device is clamped between the intermediate nut and the fastening nut, the number of parts constituting the joint is too large to improve the work efficiency. Further, there is a need for improvement of the proof strength of the connection between the long bolt and the joint device against a large load.
The present invention has been made in view of the above circumstances, and it is, therefore, an object of the present invention to improve the work efficiency in joining a wooden member to a mating member and to provide a wooden member joint structure having high resistance against a load which is repeatedly applied alternately in opposite directions.